1. Field of Art
This invention relates to an agricultural harvesting machine provided with feeder means for feeding harvested crop material to crop processing means. More particularly it relates to feeder arrest means for immediately arresting said feeder means upon detection of foreign objects and means for ensuring the good operative condition of these arrest means.
2. Description of Prior Art
It is well known in the art to provide agricultural harvesting machines, such as forage harvesters, with an apparatus for detecting foreign material in the stream of crop material which is being fed to a crop processing unit, such as a rotating cutterhead, cooperating with a stationary shear bar. Such apparatus may be a metal detector as described in European patent application 0,102,665. The signal generated by this detector is fed to feeder arrest means, which provokes an is immediate stop of the means feeding the crop material to the cutterhead. This prevents stray metal objects, which were picked up from the field, from reaching the cutterhead and causing serious damage to the knives and the shear bar. Portions of damaged knives might even get detached and cause even worse damage to other sections of the crop processing unit or the rest of the harvester.
Conventionally, the feeder arrest means comprises a ratchet wheel mounted on a drive line portion of the feed rolls and a pawl which is positioned to engage this ratchet upon detection of metal. In U.S. Pat. No. 4,296,591, the pawl is pulled towards the ratchet by a spring, while an actuated solenoid is holding the pawl away from the ratchet periphery. Upon detection of a foreign object the current to the solenoid is cut and the spring pulls the pawl into engagement with the ratchet, thereby halting the feed rolls. When an electrical failure would occur in the circuitry to the solenoid, or when the solenoid itself would go out of order, the solenoid will turn passive and the pawl will be activated by the spring. This prevents electrical failures which would pass unnoticed and foreign objects would still be permitted to be grasped by the cutterhead.
In this type of arrest means, the reaction speed and the effectiveness of the pawl are determined by the choice and the pretension of the spring. When such apparatus is used in high capacity harvesters equipped with wide cutterheads, stronger springs are required, which in turn dictate the use of stronger solenoids, having a larger actuation current.
Therefore it has been proposed to reverse the actions of the spring and the solenoid and to make the spring hold the pawl away from the ratchet, while the actuation of the solenoid brings the pawl into engagement with the ratchet wheel. In this configuration the application of a high current to the solenoid is restricted to the actual actuation interval of the feeder arrest means. However, a failure in the solenoid or its circuitry will not be detected, as the spring is still precluding immediate engagement of the pawl with the ratchet wheel. The operator will not be aware of such failures and may still erroneously presume that the harvesting machine is still capable of preventing the ingress of foreign objects.
It therefore is an object of the present invention to provide a feeder arrest means, which on the one hand can be used with large capacity harvesters, and on the other hand comprise safety features, which preclude that a failure to the actuation system of the arrest means would pass unnoticed, so that the harvesting operation might be continued and possible ingress of a foreign is object might cause substantial damage to the cutterhead.